“We wanted a historic house that needed lots of work,” said Mr. Giffen, 70, who ran a company in Alberta that handled disaster recovery. “We wanted to make it ours.”

The house was designed by architect Samuel MacClure for a cold-storage entrepreneur named Biggerstaff Wilson. The property had only one additional owner until 2010, when a local developer purchased the nearly 2-acre lot and carved off about a third of the land to build six townhouses, leaving the mansion untouched.

When the Giffens bought the home in 2011 for 1.325 million Canadian dollars, or about US$1.059 million, the 9,300-square-foot mansion sagged, the facade’s plaster was crumbling, the wood paneling in the great hall had turned black and the living-room windows were obscured by stained silk curtains.

Today, the three-story home has seven bedrooms, seven full baths, two half-baths, an elevator, a detached garage and an attic suite with a kitchenette.

The couple had two main goals: return the main floor to its prime, and thoroughly modernize the second floor and attic space.

“Their approach to it was to maintain as much of the character as possible,” said Rus Collins of Zebra Group, a Victoria design firm.

Mr. Collins took about six months to complete architectural plans for the transformation, partly guided by original blueprints. Construction started in February 2012, headed by Mike Miller, president of Abstract Developments. The bulk of the project took about 18 months and cost $1.3 million.

The couple replaced outdated electrical, plumbing and heating systems, and straightened one side of the house. They spent about $60,000 on the basement to create uniform 8-foot ceilings, and about $33,200 to seismically engineer a new interior foundation.

In the 14-foot-high great room, which has a fireplace and arched stained-glass windows, Abstract’s team stripped the blackened walls and staircase, revealing honey-colored wood.

The kitchen, a former servants’ room, had a linoleum floor, a potbelly stove and a water cistern. An alcove below the ceiling was stuffed with old slippers. “No hidden money from a bank robbery or anything exciting in the walls. No, we found about six pairs of old slippers,” said Mrs. Giffen, 66, a retired teacher.

They gutted the kitchen and butler’s pantry, adding new hardwood floors ($1,600), cabinetry ($39,200), countertops ($13,900) and appliances ($13,500). It now has two farmer’s sinks and a dog-washing station in an adjacent mudroom. Mrs. Giffen’s favorite part is a $2,000 island made from a tabletop found in the basement.

On the 2,200-square-foot second floor, what was once six bedrooms sharing a bathroom, a powder room and a room with only a tub was transformed into four en suite bedrooms and a laundry room. The couple refurbished the claw-foot tub for their master bath.

But it was the 1,860-square-foot attic, an unfinished space with 44-foot floor planks, that underwent the most dramatic change. It is now a two-bedroom, two-bathroom suite with a kitchenette and skylights.

The attic was given a drastic makeover, including adding this bathroom.

One of the biggest challenges was the house’s historic designation, which blocked changes to the exterior without city approval. To build the two-car garage, done in a similar Tudor Revival style, the couple got about two dozen neighbors to support their city application.

Adding an elevator required a 5-by-5-foot extension and bringing a shallow back staircase to code. In the process the Giffens discovered parts of the foundation had turned to sand, necessitating the concrete wall.

In another case, an antique treasure was uncovered: stained-glass pocket doors buried in the wall between the living and dining rooms.

KEY COSTS

Plumbing, in-floor heating, natural-gas system: $64,800

Stripping and refinishing wood on main floor: $15,300

Kitchen and butler’s pantry: $72,000

Redoing the basement: $60,000

Attic redesign: $68,000

Permit fees: $7,000

New garage: $71,100

Other historic gems include intricate plaster medallions that adorn the main-floor ceilings and old window glass that retains barely perceptible ripples.

The bird-patterned wallpaper in the dining room came to charm the Giffens, who saved it for a nook. “They grow on you after a while,” Mrs. Giffen said.

The Giffens have decorated the home with a patchwork of second-hand pieces. Bathroom sinks are mounted in retrofitted wood dressers. A chandelier in the entryway came from a contractor’s new house. “People were pleased with what we were doing, so they often tried to help us,” Mr. Giffen said.

The Giffens, who primarily live in Edmonton, have been visiting the home for about five years, slowly putting on finishing touches. Their next project? An overgrown rose garden.

“We don’t need any more spaces,” Mrs. Giffen joked. “If you make a finished room, you have to clean it.”

Originally appearing in the Wall Street Journal (https://www.wsj.com/articles/forget-downsizing-lets-rebuild-a-mansion-1502894014)